Interproton distances commonly used in solution structure refinements of biological macromolecules are measured by the nuclear Overhauser effect (nOe), typically observable only for interproton distances <5 A. The lack of longer-range distance constraints (>>5A) does not normally affect the solution structures of proteins, since folding brings distant primary sequence residues within 5 A of each other. In duplex DNAs and some RNAs, however, the secondary structure is primarily onedimensional with protons on each residue exhibiting nOe's only to protons on adjacent residues in primary sequence or within base-pairs. The lack of tertiary structure, coupled with the inability to determine long-range distance constraints, leaves the solution structures of many duplex oligonucleotides underdetermined. To address this concern, we have site-specifically modified a duplex undecamer (dCTCTCGGTCTCGAGACCGAGAG) with cis-[Pt(NH3)(4AT)Cl21 (where 4AT = 4an-tinoTEMPO). This platinum compound is a paramagnetic analog of the potent anticancer agent cis[Pt(NH3)2CI21, cisplatin. Incorporation of a stable unpaired electron into an otherwise diamagnetic system induces distance-dependent relaxation of each proton by the localized unpaired electron spin density. Our work focuses on the analysis of this relaxation to determine long-range (-10-20A) electron-proton distances in this paramagnetic duplex. Restrained molecular dynamics refinements of [unreadable]this DNA structure constrained with these long-range distances in addition to interproton (nOe) distances are in progress to determine the distortion of the DNA duplex which is induced upon platinumbinding. Multidimensional homonuclear and heteronuclear NMR experiments are required to determine the interproton (short-range), dihedral, and paramagnetic (long-range) constraints for this structure determination. Because the implemenation of these experiments requires specialized hardware and software such as the use of composite pulses, field gradients and nonstandard pulse trains that are otherwise not available to our laboratory, the facilities and personnel at the FBML are critical to the success of this NMR project.